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If you run iDefrag and find that your external hard disk doesn’t appear in the list on the left hand side of iDefrag’s window, while it is easily visible in Finder and Disk Utility, the most likely explanation is that you purchased a generic disk (rather than one specifically marketed for use with a Mac), and haven’t reformatted it. As a result, it is very likely formatted using the FAT32 or exFAT filesystems, for use with a Windows PC.
iDefrag is a Mac defragmenter, and as such supports HFS and HFS+, but not FAT32 or exFAT. If you are using your external disk with a Windows PC, you can of course use the free tools available with Windows to defragment it. Otherwise, we recommend that you consider reformatting the disk (with Disk Utility) as HFS+ (Mac OS Extended, Journaled), which will result in better performance and a more Mac-like user experience.
Posted by alastair at 2016-Jan-25 13:01:19 UTC. Last updated 2016-Dec-05 14:12:54 UTC.